Visible light has drawn recent interest as a new means of communication with recent developments in solid-state lighting that make it easier to accurately control light characteristics. Optical free space communications, i.e. visible light (VL) and infra-red (IR) communications, for the selection and advanced control of light sources has previously been proposed, and will be referred to as coded light (CL). The light emitted from a lighting device or luminaire, employing coded light comprises a modulated part (which for the human eye is invisible) associated with coded light comprising information messages. The emitted light also comprises an un-modulated part associated with an illumination contribution.
A visible light communications standard that is currently being developed is based on the existing IEEE 802.15.4 standard. In the existing IEEE 802.15.4 standard for wireless communication, devices may be grouped into a so-called personal area network, PAN. A PAN has an identifier that is two bytes long; and a device in a PAN may have a two-byte address assigned to it. Every device also has an eight-byte address. This eight-byte address is typically assigned to the device during manufacturing. If a device is not assigned to a PAN a default PAN identifier is used.
The existing IEEE 802.15.4 standard defines a medium access control, MAC layer. The MAC has a header which in turn has a frame control field, in which there are five bits that signal the way the source and destination addresses of a packet are transmitted in the MAC header. Two bits indicate the destination addressing mode, DAM. These two bits can take the decimal values 0, 1, 2, and 3. The value 0 means that neither the destination's PAN identifier, nor its address are transmitted. According to the existing IEEE 802.15.4 standard this implies that a source PAN identifier address must be present, unless the packet is a beacon or an acknowledgement (as indicated elsewhere in the frame control field), and that the packet is intended for the PAN coordinator of the PAN of which the identifier is transmitted in the source. The value 1 is reserved, and shall thus according to the existing IEEE 802.15.4 standard not be used. The value 2 means that the destination's PAN identifier is transmitted, as well as its two-byte address. The value 3 means that the destination's PAN identifier is transmitted, as well as its eight-byte address.
There are also two bits that indicate the source addressing mode, SAM, with similar meaning. If the source address is omitted, the packet must be an acknowledgement (as indicated elsewhere in the frame control field), or it must be sent by the PAN coordinator. A fifth bit, named ‘PAN ID Compression Subfield’ may be set to 1 if both source and destination addresses are present, which then indicates that the PAN identifiers of the source and destination are the same, and that therefore only the destination PAN identifier is transmitted and the source PAN identifier is omitted.
As noted above, a visible light communications standard (whereby the devices of the PAN preferably are luminaires and communicate by means of coded light) that is currently being developed is based on the existing IEEE 802.15.4 standard. The personal area network thereby becomes a visible are network, VAN.